1. Field of the Invention
This invention relates to non-linear optical components forming the basic building blocks of information technology of the future. Non-linear optical thin films formed on gallium arsenide, aluminum gallium arsenide, indium gallium arsenide, and Si semi-conducting substrates have many potential applications in integrated optics. With this technology, semi-conducting diode lasers, non-linear optical devices such as spatial light modulators, frequency doubling second harmonic generators, and photodiode detectors can all be integrated on the same semi-conductor substrate, which has been found to enhance system performance while simultaneously lowering the cost of production and manufacture.
Practical applications of promising non-linear optical thin film device technology for integrated optics critically depends on the successful development of non-linear optical thin films with desirable optical properties. These films must exhibit a high degree of structural and compositional quality since these properties directly aid in providing the desired non-linear electro-optic properties. To this end, the invention described herein is directed to a non-linear optical thin film layer system and a method for producing the same.
In particular, this invention pertains to the integration of a non-linear optical thin film layer having a gallium-arsenide substrate. Still further, this invention relates to a non-linear optical thin film layer system in which the non-linear optical thin film layer is integrated with an encapsulated gallium-arsenide substrate, where the encapsulation provides a chemical barrier against arsenic contamination of the non-linear optical thin film layer.
Still further, this invention relates to a non-linear optical thin film layer which is integrated with an encapsulated gallium-arsenide substrate through a plurality of epitaxially grown and contiguously interfacing transitional buffer layers, where the buffer layers define a lattice constant matching criteria between a lattice constant of the encapsulated gallium-arsenide substrate and the lattice constant of the non-linear optical thin film layer.
Further, this invention directs itself to a non-linear optical thin film layer system which provides for a gallium-arsenide substrate having a contiguously interfacing encapsulating layer deposited on the lower surface, peripheral sides, and upper surface peripheral region of the gallium-arsenide substrate.
Additionally, the non-linear optical thin film layer system includes a second encapsulating layer and buffer layer epitaxially grown and contiguously interfacing with the exposed upper surface of the gallium-arsenide substrate and the encapsulated upper surface peripheral region of the gallium-arsenide substrate. A second buffer layer is epitaxially deposited on an upper surface of the second encapsulating layer/buffer layer whereby the second encapsulating layer/buffer layer and second buffer layer provide a monotonically decreasing lattice constant which approximates, at the second buffer layer, the lattice constant of the non-linear optical thin film layer deposited thereon.
Still further, this invention pertains to a pair of first and second encapsulating layers which prevent arsenic contamination of a non-linear optical thin film layer deposited at temperatures above the dissociation temperature of the gallium-arsenide substrate. Additionally, this invention describes a non-linear optical thin film system incorporating a plurality of layers formed on a gallium-arsenide substrate where at least a pair of first and second encapsulating layers hermetically seal the gallium-arsenide substrate from an external environment.
2. Prior Art
In the prior art, deposition of epitaxial ferroelectric optical materials, particularly oxides, on gallium-arsenide substrates for use in systems has been addressed. In some prior art techniques, a magnesium oxide composition layer is suggested for use as a buffer layer between the gallium-arsenide substrate and a ferroelectric oxide composition. It is known that precautions must be taken to avoid arsenic contamination once the wafer has been capped with a magnesium oxide composition layer. However, such prior art fails to show or suggest the use of an encapsulating layer to contiguously encapsulate the lower surface, side surfaces, and upper surface peripheral regions of a gallium-arsenide substrate for minimizing contamination. Additionally, such prior art does not show or suggest that an encapsulating layer may advantageously be formed of silicon nitride.
Further, such prior art fails to disclose or suggest deposition of a magnesium oxide composition layer on the upper surface of the gallium-arsenide substrate including deposition over an encapsulated peripheral region of the substrate's upper surface.
Additionally, such prior art does not teach or suggest the deposition of a second buffer layer on the magnesium oxide layer for the purposes of lattice matching between layers and for covering defects in the magnesium oxide composition layer. Even further, the description fails to suggest the particular optical non-linear thin film layer compositions of the present invention.
In a prior art Publication entitled "Phase Composition and Microstructure as a Function of Deposition Conditions for Potassium Titanate Niobate Thin Films Grown by Pulse Laser Deposition," by Cotell and Leuchtner, there is provided a description of pulse laser deposition of potassium tantalate niobate (KTN) films on magnesium oxide substrates using segmented targets consisting of KTN and potassium nitrate. The disclosure made by this prior art Publication fails to show or suggest any integration with a gallium-arsenide substrate, the encapsulation of such a substrate to prevent arsenic contamination of the optical thin film, the use of a strontium titanate buffering layer, or a combination of these elements for the purposes and objectives of the subject invention concept.
A further prior art Publication entitled "Pulsed Laser Deposition of Stoichiometric Potassium-Tantalate-Niobate Films from Segmented Evaporation Targets," by Yilmaz, Venkatesan, and Gerhard-Multhaupt, discusses the preparation of epitaxial KTN films on strontium-titanate substrates by means of pulse laser deposition. Absent from this disclosure are any teachings with respect to the integration of the non-linear optical thin film layer with an encapsulated gallium-arsenide substrate (or indeed a gallium-arsenide substrate without encapsulation), the use of a metal oxide buffering and encapsulating layer, or a combination of these elements commensurate with the present invention.
Further, the prior art fails to show or suggest the combination of composition layers comprising the non-linear optical thin film layer system to which the present invention is directed. Even further, the prior art fails to show or suggest the particular method steps, and their combination, for producing the non-linear optical thin film layer system to which the present invention is directed. For example, the prior art fails to show or suggest the particular steps for depositing the various layer compositions in the non-linear optical thin film layer system of the present invention, and further fails to teach or suggest the important cooling step required subsequent to the high temperature deposition of the non-linear optical thin film layer.
By encapsulating the gallium-arsenide substrate using first and second encapsulating layers, it has been found that the high temperature epitaxial deposition of a non-linear optical thin film layer can result in a high quality optical thin film which exhibits the desired non-linear optical properties for use in an integrated optics system. These encapsulating layers, which prevent arsenic contamination of the optical thin film layer, are used in the present invention in combination with lattice matching buffering layers to provide an excellent growth template on which a highly oriented, high quality, non-linear optical thin film layer may be deposited at high temperatures.